Thermal conversion of reduced crudes



Sept. 11, 1956 W C, OFFUTT ET AL THERMAL. CONVERSION OF REDUCED CRUDESFiled Deo. 20, 1951 Nml mN NN A .W MEN United States Patent O THERMALCONVERSION F REDUCED CRUDES William C. Ofutt, "Edgewood, Paul Siecke,Mount Lebanon Township, Allegheny County, andv Harold Beuther, PennTownship, Allegheny County, Pa., assignors, by direct and mesneassignments, to Guif '()il Corporation, Pittsburgh, Pa., a corporationof Pennsylvania Application December 20, 1951, Serial No. 262,566 3Claims. (Cl. v196-50) 'Ihis invention relates to a thermal conversionprocess, and more particularly to a process whereby exceptionally heavyfractions of crude petroleum are converted to more valuable products bythermal conversion.

Methods of refining crude petroleum vary considerably depending upon thetype of crude oil available, the market area in which the refinerydisposes of the products, and other factors. The method probably mostfrequently employed in modern refineries involves first subjecting thecrude oil to atmospheric distillation under conditions to recoverdistillate fractions including a gasoline fraction and a furnace oilfraction having an end point of about 650 to 750 F. The bottoms fromthis distillation is then subjected to distillation under a vacuum toremove overhead a charging stock for conventional catalytic crackingsuch as fluid catalytic cracking or moving bed catalytic cracking. Inthis last distillation step it has been the practice to produce a vacuumbottoms which contains not only the asphaltic constituents initiallypresent in the crude oil but also certain of the heavier oil fractions.This final reduced crude has then generally been disposed of as a heavyfuel oil referred to as No. 6 or Bunker C fuel oil.

Despite the fact some of the oil constituents of the crude are generallyretained in this bottoms product, it is normally too heavy and viscous amaterial to be sold as such, particularly if the vacuum distillation hasbeen carried out so as to yield an eiiicient amount of catalyticcracking charge stock. In order to convert this heavy material to asalable product, it has been necessary to dilute it with a lighter oil,usually catalytic cycle stock which is'frequently about 650 F. end pointmaterial; in other words, a No. 2 fuel oil, which would demand arelatively high price if sold as such. Inasmuch as a No. 6 fuel oil is alow-priced material, it has long been the desire of refiners to reducethe production of this product while increasing the production of morevaluable products obtainable from the crude oil.

One procedure that has been given consideration nvolves subjecting thevacuum bottoms product to thermal conversion to accomplish conversion ofa part of the product into gasoline and the remainder into a lessviscous material than the charge stock. However, so far as known,attempts to subject the vacuum bottoms product obtained in theconventional operation to thermal cracking or visbreaking at temperatureabove 900 F. in the equipment generally employed for thermally crackingor visbreaking lighter charge stocks, have not been successful. This isbecause such products obtained from the types of crudes handled in themajority of domestic refineries have yielded an inordinate amount ofcoke and gas if subjected to thermal conversion under con- .ditionssufficiently severe to obtain the desired conversion of the chargestock. Thus, if such a stock is subjected to visbreaking at atemperature sufiiciently high vto cause adequate conversion of thestock, such as conversion resulting in the production of 8 per cent ormore gasoline by volume of the charge, the formation of coke is such asto reduce to an uneconomically short time the period during which theconversion unit can remain on stream. On the other hand, if the maximumtemperature to which the charge is heated is reduced to a point at whichcoke formation permits long on-stream periods, the amount of conversionis substantially reduced.

The coke deposited during thermal conversionl operations of the typeunder consideration is a hydrocarbonaceous material in which the ratioof carbon to hydrogen is extremely high. It has long been accepted. thatunder a given set of operating conditions the amount of coke produced inthermal conversion operations will vary generally in accordance with thecarbon-hydrogen ratio 0f the hydrocarbon compounds making up the chargestock, and this has been confirmed by numerous experimental andcommercial thermal operations on heavy gas oils and on typical reducedcrudes containing asphaltic and heavy oil constituents of the originalcrudes. A recognized indication of the carbon-hydrogen ratio of a heavyoil, and therefore the coke-making tendency of the oil, is the Conradsoncarbon residue number of the oil. Thus it is accepted that bycontrolling the degree of reduction of a crude so as to produce areduced crude having a relatively 10W Conradson carbon residue number, acharge stock suitable for thermal conversion without the production ofundesirable amounts of coke can be obtained.

The present invention is based upon the discovery that by removingsubstantially more of the lighter compoundsv in reduced crude oils thanis the conventional practice,

the resulting residual product can be successfully visbroken in asingle-pass operation by flowing the reduced crude through a thermalconversion zone under conditions including zone exit temperature ofabout 900 to about l000 F., which is applied to a longer residuum of thesame crude oil, would result in the production of coke and gas at ratessuch as to reduce to an uneconomically short period the time duringwhich the operation could be continued. The product of the processcomprises gasoline and a residue substantially less viscous than thecharge material.

The extent of reduction of the crude required to produce a charge stocksuitable for use in the process of the invention cannot adequately bedefined as a percentage of the crude because of the Wide variance in thecomposition and properties of crudes from different oil fields. In thecase of a highly paraiiinic crude, a bottoms product consisting of only5 to 6 per cent by Weight of the crude might be too light for effectiveuse, Whereas in the case of a crude containing a substantial amount ofasphalt, a bottoms product consisting of as high as 30 per cent of thecrude might be suitable. We have found that reduced crudes which have aConradson carbon residue number of at least 18, an A. P. I. gravitybelow 10, and a viscosity, S. U. S. at 210 F., of at least 6000 can beemployed successfully in the present process. v y

While it is not intended to limit the present invention to anyparticular theory, the research Work leading to the development of theinvention has indicated that the difficulties experienced in the past inattempting to visbreak deeply reduced crudes were due to the fact thereduced crudes employed contained oil components probably largelyparainic in nature. These components,

although lighter and having a smaller carbon residue number than theremainder of the reduced crude, apparently were converted readily tocoke and may have tended to direct conversion of the remainder of thereduced crude towards high coke formation. Removal of lightercornponents in accordance with the invention has resulted in a chargestock which can be visbroken at temperatures above 900 F. without theproduction of 'excessive amounts of coke. .t .1 v;

The deeply reduced crude charge stock for the present process ispreferably prepared by subjecting the crude oil to conventionaldistillation at atmospheric pressure to remove overhead as distillatethe gasoline, kerosene, and furnace oil cuts; for example, the fractionsboiling below a selected temperature such as 650 or 750 F. The bottomsfrom this operation is then subjected to vacuum distillation underconditions to pass overhead an amount of catalytic cracking chargingstock in excess of that conventionally produced from such a bottomsmaterial and to yield a vacuum bottoms or tar having the characteristicsdiscussed above; i. e., a Conradson carbon residue number of at least18, an A. P. l. gravity of below 10, and a viscosity, S. U. S. at 210F., of at least 6000. The production of a vacuum bottoms of this type ispreferably accomplished by increasing the vacuum in the distillation,but also can often be accomplished by increasing the heat content of thecharge to the vacuum still. The necessary adjustment of conditions toobtain the desired extent of reduction of the crude is fully within theskill of an operator of this type of equipment.

The vacuum bottoms constituting an exceptionally deeply reduced crude isthen passed to a thermal cracking unit of conventional design comprisinga conversion coil in a cracking furnace and means such as gas or fueloil burners positioned in the lower part of the furnace. The conditionsof the operation, including heat input, rate of ow of charge through thecoil, and time, are adjusted so that the temperature of the charge atthe outlet of the coil is about 900 to about 1000 F., preferably about920 vto about 980 F.; and the charge to the coil is converted togasoline (C4s up to 400 F. end point) in an amount equal to at least 8per cent and preferably not more than per cent by volume of the charge.These conditions are preferably selected from within the ranges: coilvolumes of about 0.012 to about 0.050 cubic feet of coil volume above750 F. per barrel throughput per day; linear velocity of about 0.1 to 10feet per second; pressure of vabout 50 to about 1000 pounds per squareinch gauge (pressure is not an important factor because the extremelyheavy charge will be in liquid phase and it is only towards the end ofthe coil that lighter hydrocarbons are formed in any substantialamount); and a heat input of about 5000 to about 15,000 B. t. u.s perhour per square foot of outside heating surface.

A preferred embodiment of the invention will be understood more fully byreference to the accompanying drawing, the single figure of which is adiagrammatic representation of a suitable system for carrying out theembodiment. The drawing will be described in connection with thetreatment of a typical Westv Texas crude oil. The lcrude oil isintroduced into the system through a v'alved line 1 leading to aconventional furnace 2 wherein the crude is heated'to a suitableelevated temperature such as a temperature of about 650 to 750 F. Fromthe heater Vthe crude flows through valved line 3 to an atmosphericdistillation column d. As is well known, such a distillation column maybe operated so as to separate the crude into a variety of products;however, in this instance the column is operated so as to obtain the C4and lighter hydrocarbons as overhead products which are passed throughline 5, a 300 F. end point gasoline which is passed through line 6, a300 to 400 F. naphtha which is passed through line 7 and a 400 to 650 F.furnace oil v'fraction which is passed through line 8. Operating in thisway the bottoms product will comprise of the order of about per cent ofthe crude and this product is removed through line 9 leading to a heater11 which supplies sufficient heat to the bottoms to raise this productto a temperature of about 700 to about 800 F. The lheated material thenpasses through line V12 leading to a vacuum tower 13.

This tower -is operated as previously described in order to produce as avacuum bottoms or tar a deeply reduced crude having the characteristicsoutlined above. To accomplish this on the bottoms from the atmosphericdistillation column, an amount equal to about 30 volume per cent of theoriginal crude, is passed overhead from the vacuum tower through line i4as charge to a conventional catalytic cracking unit and auxiliaryequipment indicated generally at 15. Thus, the vacuum bottoms comprisesabout 10 volume per cent of the crude and is a product having theproperties specified above.

The vacuum bottoms is passed through line 16 leading to a conventionalvisbreaking or thermal cracking furnace indicated generally at 17. Inorder to move the vacuum bottoms from the vacuum `tower to the furnace17 and also lto provide the desired pressure on the oil in the furnace,a pump 1S is employed in line 116. `In the furnace the vacuum `bottomsis passed through `coil 19 and is heated by means of a plurality ofburners 21, disposed in the lower portion of `the furnace. In thearrangement shown, the furnace comprises a convection heating sectionindicated generally at Z2 and a radiant heating section indicatedgenerally at 23. The pressure in the coil may vary, for example, it maybe labout 50 to about 1,000 pounds per square inch, and preferably isabout to 600 pounds per `square inch. In the coil the charge issubjected to visbreaking under conditions such that the coil loutlettemperature is about 900 to 1000 F., preferably about 920 to about 980F., and the coil volume is about 0.020 to about .035 (cubic feet of coilvolume above 750 F. per barrel of throughput per day).

The product from the visebreaking furnace 17 is removed from the furnacethrough valved line 26 leading to a fractionator 27. in this embodimentthe fractionator is operated so as to pass overhead the 400 F. end pointgasoline and lighter materials through a line 28. This overhead productis sent to la stabilizer, not shown, wherein Css through 400 F. endpoint gasoline is separated from the Cas yand lighter gases. Thegasoline removed through this line under the conditions stated willcomprise of the order of 8 to 18 volume per `cent of the vacuum bottomsand the bottoms product will comprise about 92 to 82 volume per cent ofthe vacuum bottoms.

ri'he bottoms product is removed through valved line 29 to a mixingvessel Si. Since the product alone will be too heavy for sale as No. 6fuel oil, it is mixed with catalytic cracking cycle stock from `thecatalytic cracking unit i5 through line 32.

In order that this embodiment of the invention may `be understood morefully, ythere i's `presented below in Table l data obtained in a series'of runs in which the charge to `the visbreaker was a vacuum bottomscomprising 9.9 volume per cent of the West Texas crude.

in all of the runs for which data are given in the table, cokedeposition was insignificant and the runs were not extended to evaluatethe advantages of the operation with respect to duration lof on-streamperiods. The inspections for the 9.9 volume per cent West Texas reducedcrude were as follows:

Gravity, API f 8.5 Viscosity, SUS at 210 F. 7932 B. S. 8: W., per cent0.1 Conradson carbon residue, per cent 19.8 Sulfur, per cent 2.90 Pourpoint, F. 100 Melting point, F. (R. & i3.) 1717 Penetration (D5) 168 Thegravity, viscosity, and Conradson carbon residue values given in thistable were determined in accordance with the test methods given in ASTMStandards on Petroleum Products and Lubricants November, 1950. Thegravity test bears ASTM designation DZ87-39; the viscosity test, theASTM designation D88-44; andthe Conradson carbon residue test, `thedesignation 13189-46.

light catalytic cycle stock having a 31.2. This oil is referred to ascutting oil in the folgravity, API, of

F. It is pointed out that these runs and the runs described later inthis specification Were carried out in pilot plant equipment. It is agenerally accepted rule that the periodv during which a commercialvisbreaking plant can remain lowing Table I.

Table I Charge to Visbreaker Furnace 9.9 Vol. Percent West Texas CrudeRun N o Charge A B C Period 1 2 1 2 1 2 Operating Conditions:

Coil Outlet Temp., F 920 940 960 980 950 950 Coil Pressure, p. s. i. g200 200 200 200 600 11 000 Coil Volume above 750 F. (Ou. lit/Bbl.

throughput/dar) o. 019 o. 020 o. 020 o. 02o o. o16 o. 014 Length of TestPeriod, hours 6 6 6 6 6 12 Yields, Vol. Percent of Charge to Furnace:

' 1.5 2.0 2.0 2.2 2.3 1.9 9. 3 10. 7 12. 3 17. 3 18. 2 15. 3 4.8 5.3 4.75.3 8.6 6.0 400 BFI-Bottoms 91. 6 89. 8 88.0 84. 2 83. 4 87. 0 Fuel OilBlends (200 SFS at122 F Yield of Bottoms (Vol. Percent of Crude) 400F.+Bottoms of Visbroken Products. 9. 9 9. 0 8. 9 8. 7 8. 3 8.3 8. 6Cutting Oil Required to Make Fuel Oil (Vol.

Percent of Crude) 4. 9 2.8 2. 7 2. 6 2. 6 2. 3 1. 9 Yield 0f Fuel Oil(Vol. Percent of Crude) 14. 8 11.8 11.6 11.3 10. 9 10.6 10.5 Fuel OilInspection Data:

Gravity, API 15. 0 12. 4 12.4 l1. 5 10. 8 11. 5 12. 3 Viscosity, SUS at130 F- 1, 400 1, 630 1, 440 1, 680 1, 710 1, 550 1. 310 Viscosity, SUSat 210 F- 192 179 161 223 274 146 158 Viscosiry, SFS at 122 F-- 194 214202 210 174 207 185 B. S. d: W., Percent trace 0. 05 O. 4 0.6 1. 4 0.20.1 Carbon Residue, Percent (Conradson) 14. 9 18. 5 21. 2 21.9 22. 721.9 20. 8 Sulfur, Percent 2. 14 2. 38 2. 46 2. 47 2. 56 2. 62 2. 32Pour Point, F 10 20 30 25 45 45 25 Flash Point, "F 230 230 225 225 230230 230 Sediment by Extraction, Percent (D473) 0.01 0.01 0.06 0.15 0. 40.0.14 0.04

Each of the runs A, B, and C was a ation over the two periods named,although the products were analyzed at the end of cach portant cokedeposition occurred and the light gas production was satisfactory duringthe runs.

parent that each run could have been period many times as long as theperiods named in the table, and this despite the facts that the reducedcrude charge was an extremely heavy material and that the coil outlettemperatures were substantially above 900 continuous operperiod. No im-It was apcontinued for a 40 products obtained from the crude.

the reduced crude charge was employed for making heavy fuel oil, 14.8per cent by volume of the original crude For example, when Table IlCharge to Vlsbreaker Furnace Charge I Charge II Run No Charge D Charge EI II Duration of Run, Hours 27 72 Period- 1 1 2 3 Remarks-Coil ConditionCoked OK 0 K OK Operating Conditions:

Coil Outlet Temp., F Coil Pressure, p. s. i. g Coil Volume above 750 F.(Cu. Ft./Bbl.

throughput/da C Length of Test Period, hours Ylelds, Vol. Percent ofCharge to Furnace:

Gas (C3 and Lighter) (FOE) O4 400 F. Gasoline 300400 F. Naphtha 400F.+Bottoms Fuel Oil Blends (200 SFS at 122 F.).

Yield of Bottoms (V ol. Percent of Charge) (400 F.+Bottoms of VisbrokenProducts) Cutting Oil Required to Make Fuel Oil (Vol. Percent of Charge)Yield of Fuel Oil (Vol. Percent of Charge) Fuel Oil Inspection Data'Gravity, API Viscosity:

SUS at 130 F- SUS at 210 F BFS at 122 F. B. S. & W., PercenL CarbonResidue, Percent (Conradson) Sulfur, Percent Pour Point, F Flash Point,F Sediment by Extraction, Percent (D473) had to be disposed of as heavyfuel oil. Moreover, in order to produce a salable fuel oil from thereduced cru-de charge, it was necessary to employ 4.9 per cent by volumeof the cutting oil, which was a light TCC cycle stock suitable forincorporation -in a No. 2 fuel oil. Proceeding in accordance with theinvention reduced the total amount of heavy fuel oil to from 11.8 to10.5 volume per cent of the crude, and perhaps more important, reducedthe @D Gravity, API 5.4 Viscosity, SUS at 210 F 16,200

Conradson carbon residue, per cent 22.0 Sulfur, per cent 5.30 Pourpoint, F 110 The oil used to cut the various bottoms product was a lightcatalytic cycle stock having a gravity, API, of 31.2.

cutting oil required to an amount from 2.8 to 1.9 vol- This oil 1sreferred to as cutting oil 1n Table III.

Table III Charge to Visbreaker Furnace 17.7 Vol. percent Kuwait CrudeRun No Charge F G H I .T K L M Duration oi Run 48 21 13 12 10Remarks-Coil Condition. OK OK OK OK OK Operating Conditions:

Coil Outlet Temp., F.- 925 900 930 900 900 Coil Pressure, p. s. i. g 20020 200 200 200 Coil Volume above 750 0.0300 0. 0247 0. 0246 0. 03030.0343 Length of Test Period, hours 4S 8 8 Yields, Vol. percent ofCharge to Furnace:

Gas (C3 and Lighter) (FOE) 1.9 2.7 1. 5 1.6 1.9 1.1 1.4 O4 400 F.Gasoline 14. 2 17 1 18.3 12. 3 10. 9 14. 9 10. 1 11.6 300-400 F.Naphtha. 6. 9 4.3 3. 2 3.0 3.0 3.8 400 F. -l- Bottoms 87. 3 85.1 83. 590.6 91. 0 87. 1 91.6 90 2 Fuel Oil Blends (200 SFS at 122 E):

Yield of Bottoms (Vol. percent of Crude 400 F. Bottoms ct VisbrokenProducts) 17. 7 15. 5 15.1 14.8 16.1 16.1 15.4 16. 2 16.0 Cutting OilRequired to Make Fuel Oil (Vol. percent o Ctude) 10.2 5. 5. 5 5. 4 5. 76. 3 5. 2 5. 5 5. 5 Yield oi Fuel Oil (Vol. percent of Crude) 27. 9 21.120. 6 20. 2 21.8 22. 4 20.6 21.7 21.5 Fuel Oil Inspection Data:

Gravity, API 13. 9 10. 6 9. 5 9. 6 11. 1 l1 3 9. 7 10. 5 10.7 Viscosity,SUS at 130 F l, 450 1, 294 l, 511 1, 358 1,236 1, 375 1, 475 1, 486 1,523 Viscosity, SUS at 210 F.. 20 164 166 152 162 175 174 182 183Viscosity, SFS at 122 F.. 184 172 205 192 171 187 203 202 195 B. S. &W., percent trace trace 0.05 0.05 trace trace trace trace trace CarbonResidue, percent (Conradson) 14. 6 20. 5 21. 5 21.9 19.9 20. 1 22.0 20.421.1 Sulfur, percent 3. 71 4. 24 4. 42 4.47 4. 29 4. 28 4. 53 4. 41 4.44 Pour Point, 5 5 15 15 10 15 15 15 20 Flash Point, F 224 230 230 22524 210 196 220 1 6 Sediment by Extraction, percent (D473) 0.01 0.02 0.020.09 0. 01 0.02 0.02 0.01 0. 0 2

urne per cent of the crude. Moreover, in cach of the runs the gasolineproduced varied from 9.3 to 18.2 per cent by volume of the reduced crudecharge.

To illustrate the importance of extremely heavy reduced crudes as chargestocks in the process of the invention, there is presented in thefollowing,y Table 1I the Charge 1 l`Oharge II Gravity, API 9.0 5. 6Viscosity, SUS at 210 F 3, 607 49, 960 Conradson Carbon Residue,percent.-. 19. 0 26. 2 ISulfur, percent 2. 76 2. 9S Melting Point, F. (Ra 13).- 99 145 Penetration (D) 285 16 The oil used to cut the variousbottoms products Was av catalytic cycle stock having a gravity, APL of31.2. This oil is referred to as cutting oil in Table Il.

From the results set out in Table Il, it will be seen that run D usingcharge I had to be discontinued after 27 hours because of serious cokingdifficulties experienced in the coil. This is to be contrasted With runE which, although it was continued almost three times as long as run D,did not result in the formation of any serious amount of coke in thecoil'.

Additional runs in accordance with 'the invention have been made withother charge stocks. For example, successful results were obtainedemploying as the charge stock a 17.7 volume per cent reduced Kuwaitcrude. The inspections for this reduced crude were as follows:

It will be seen that practice of the present process on the heavyreduced crude of Table III substantially reduced the amount of heavyfuel oil prepared from the Whole crude and correspondingly reduced theamount of cutting oil required for blending with the bottoms to producethe heavy fuel oil. Also, although the temperatures Were as high as 955F. in these runs, the Visbreaking operation Was carried out withoutcoking in the visbreaker coil. This is surprising in View of the factthat the reduced crude charge had the low gravity, API, of 5.4; the highviscosity, S. U. S. at 210 F., of 16,200; and the Conradson carbonresidue of 22.0.

The present process, when applied to the treatment of typical crudeoils, has the advantages of permitting visbreaking without heavy cokedepositions so that long onstream periods are feasible, andsubstantially reducing not only the total heavy fuel oil produced fromthe crude but also the amount of light oil such as a No. 2 fuel oilobtained as a fraction from the products of catalytic cracking requiredfor diluting the reduced crude to form the heavy fuel oil, However, whenvisbreaking bottoms fractions of certain crudes which are frequentlyreferred to as tar oils, the visbreaking operation in accordance withthe invention is successful with respect to coke Y deposition and theproduction of gasoline, but, due to the almost coal-like nature of thebottoms of the visbroken product, a substantial amount of light fuel oilis required to make a heavy fuel oil, an amount which may even exceedthat required for dilution of the charge to visbreaking to form asimilar heavy fuel oil.

-From all of the foregoing, it will be seen that the invention providesa process of visbreaking extremely heavy reduced crudes that hadpreviously been considered unsuitable for visbreaking under conditionsadequate to produce commercially valuable conversion of the charge. Ingeneral, the thermal conversion conditions are such as to yield at least8 per cent gasoline (C4/s to 400 F. end point) by volume of the reducedcrude and include a thermal conversion zone exit temperature of about900 to 1000 F. These conditions are such that when applied to a longerresiduum of the same crude oil (i. e. a residuum constituting a higherpercentage of the crude oil and having a higher API gravity than 10, alower S. U. S. viscosity at 210 F. than 6000, or a Conradson carbonresidue number less than 18) would cause the formation of coke at a ratesuch as to reduce materially the time during which this longer residuumcould be charged to the thermal conversion zone. A striking example ofthis is shown in Table II above. The viscosity of charge I was below6000 and this stock coked the conversion coil in 27 hours, whereascharge II which had a viscosity substantially above 6000 did not causesubstantial coking after 72 hours of operation.

The stocks suitable for use as charge stocks in accordance with theinvention have the characteristics: API less than Conradson carbonresidue of at least 18; and viscosity S. U. S. at 210 F. of at least6000. These characteristics represent the best practical manner ofdefining reduced crudes that crack at suticiently low rates (reactionvelocity constants) to keep coke formation low during visbreakingoperations. Reaction velocity constants of the charge stocks in Table IIshow that charge I has the higher reaction velocity constant, andtherefore, would be expected to coke more readily. In the past it wasthought that the coking rate (or reaction velocity constant) increasedwith an increase in the molecular weight of a cracking charge stock(prepared by deeper vacuum topping of the reduced crude). However, Wehave discovered that continued reduction of a crude apparently removeshigh boiling oils which have high reaction velocity constants and cokereadily. After this heavy oil is removed, the deeply reduced crude canbe visbroken without serious coke formation. Since reaction velocityconstants of reduced crudes can only be calculated after cracking datahave been determined, and the values differ depending on methods ofcalculation and equipment used, etc., the values have a relative meaningonly, and therefore they have not been employed to characterize chargestocks. As indicated above, it is believed that the characteristicsgiven constitute a means of defining stocks having suitable reactionvelocity constants.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

l. A process for the conversion of petroleum hydrocarbons comprisingdistilling from a crude oil kerosene and lighter fractions to form abottoms fraction, vacuum distilling the bottoms fraction underconditions of ternperature and vacuum to form a residuum having agravity less than 10 A. P. I., a Conradson carbon residue number of atleast 18 and an S. U. S. viscosity at 210 F. of at least 6000, andthermally cracking the residuum at a temperature in the range ofapproximately 900 to 1000 F. and a pressure of about 50 to 1000 poundsper square inch in a once-through visbreaking operation to yield atleast 8 per cent, by volume of the residuum, 400 F. end point gasoline.

2. A process for the conversion of petroleum hydrocarbons comprisingdistilling from a crude oil kerosene and lighter fractions to form abottoms fraction, vacuum distilling the bottoms fraction underconditions of temperature and vacuum to form a residuum having a gravityless than 10 A. P. I., a Conradson carbon residue number of at least 18and an S. U. S. viscosity at 210 F. of at least 6000, and thermallycracking the residuum at a temperature in the range of approximately 920to 980 F. and a pressure of about 50 to 1000 pounds per square inch in aonce-through visbreaking operation to yield at least 8 per cent, byvolume of the residuum, 400 F. end point gasoline.

3. A process for the conversion of petroleum hydrocarbons to morevolatile products comprising passing a charge stock consisting of adeeply reduced crude having an A. P. I. gravity lower than 10, aConradson carbon residue number of at least 18, and an S. U. S.viscosity at 210 F. of at least 6000 through a cracking coil, thetemperature at the outlet of the coil being in the range of 900 to 1000F., the pressure being in the range of to 1000 pounds per square inchgauge, and the volume of the coil above 750 F. being in the range of0.012 to 0.05 cubic feet per barrel of throughput per day, whereby about8 per cent to 20 per cent 400 F. end point gasoline, by volume of thedeeply reduce-d crude, is formed.

References Cited in the tile of this patent UNITED STATES PATENTS2,374,338 Dunham Apr. 24, 1945 2,416,608 Brackenbury Feb. 25, 19472,633,449 Cheney Mar. 31, 1953 FOREIGN PATENTS 200,933 Great BritainJuly 24, 1923

1. A PROCESS FOR THE CONVERSION OF PETROLEUM HYDROCARBONS COMPRISINGDISTILLING FROM A CRUDE OIL KEROSENE AND LIGHTER FRACTIONS TO FORM ABOTTOMS FRACTION, VACUUM DISTILLING THE BOTTOM FRACTION UNDER CONDITIONSOF TEMPERATURE AND VACUUM TO FORM A RESIDUUM HAVING A GRAVITY LESS THAN10* A. P. I., A CONRADSON CARBON RESIDUE NUMBER OF AT LEAST 18 AND AN S.U. S. VISCOSITY AT 210* .F. OF AT LEAST 6000, AND THERMALLY CRACKING THERESIDUUM AT A TEMPERATURE IN THE RANGE OF APPROXIMATELY 900* TO 1000* F.AND A PRESSURE OF ABOUT 50 TO 1000 POUNDS PER SQUARE INCH IN AONCE-THROUGH VISBREAKING OPERATION TO YIELD AT LEAST 8 PER CENT, BYVOLUME OF THE RESIDUM, 400* F. END POINT GASOLINE.